The proposed study will utilize existing data from 7 major longitudinal growth studies in which more than 2000 individuals were enrolled; some of these records extend for periods longer than 50 years. Use will be made also of existing cross-sectional data from some very large kindreds, from NCHS surveys, from USAF surveys and from studies in which anthropometric and densitometric data have been obtained. In addition, further serial data will be obtained from juvenile and adult participants in the Fels Longitudinal Study, including some additional variables relating to apolipoproteins and impedance. The long-term aims are to achieve more complete understanding of the natural history of body fatness and the extent to which tracking occurs in fatness and associated risk factors. This is relevant to the timing of preventive measures. Some planned analyses relate to fat patterning and probable changes with age in the associations between body fatness and frame size. Pubescent changes in body composition and the relationships between risk factors during pubescence and in adulthood will be examined. Some analyses will relate to the potential use of frame size in the interpretation of observed weight. Appropriate measures of frame size will be sought that are highly correlated with weight, but independent of fat. Reference data will be provided if appropriate. It is well-known that the management of obesity is often inefficient, if judged over long intervals. To some extent, this may reflect application of a single treatment mode to a heterogeneous group of conditions. The effective categorization of obesity requires data of many types and is unlikely to be achieved in a single study. It is expected, however, that the proposed research will provide useful findings in regard to categories based on anthropometric and body composition data. Associated with this aim correlations between impedance measurements and lean body mass will be examined and equations developed that provide estimates of body composition from anthropometric data. Other planned analyses concern associations between risk factors, e.g., blood pressure, plasma lipids, and variations in the amounts and types of body fatness and in adipocyte size. Attempts will be made to "separate" the genetic and cultural determinants of body fatness by applying path analysis to sets of data from large numbers of nuclear families.